Does Turning Off The Water Supply Affect The Boiler?

Perhaps you found a leak and need to turn off your water supply. However, you’re concerned that turning off the water supply could negatively affect your boiler. You might be worried the system will overheat (similar to boiling a kettle without water in it). 

Key Points:

  • Boilers are designed with sensors and controls that prevent damage when the water supply is turned off.
  • The three types of boilers are Combination, System, and Heat Only boilers.
  • To turn off the water supply if a leak is found, locate the stopcock, place a bucket underneath it if possible, switch off the boiler and isolate electricity at the fuse box.

While we understand the concern, you can put those worries to rest. Generally, your boiler is unlikely to be at risk of damage when you turn the water supply off, providing it’s in good working condition. We’ll explain this more in the following sections, so continue reading to learn more!

Types Of Boilers

Before we explain the specifics, let’s look at the main types of boiler systems. There are three primary types, each offering hot tap water in a slightly different way. 

In each of these systems, the water that comes out of your tap isn’t the same water that passes through the heat exchangers. The water the boiler heats is in a closed loop, so it heats, cools, and circulates continuously. The water you receive through your hot taps either comes directly from your mains, a cylinder, or a loft tank. 

Combi Boiler

Combination boilers, also known as combi boilers, are a popular option. These boilers heat water on demand, satisfying our need for instant gratification. Due to the way these boilers function, there’s no need for tanks or cylinders. 

Instead, the mains water passes through a heat exchanger circulating boiled water. The already-boiling water heats the water passing through, giving you hot water rapidly. Since this type of boiler operates without a tank or cylinder, it’s unlikely to be affected by turning off the water supply.

System Boiler

System boilers are another common option for generating hot water. Unlike the combination boiler, system boilers use a cylinder. The boiler supplies mains water to a cylinder that is heated by the hot water circulating around it. It operates somewhat like a radiator. 

The cylinder containing the water is under pressure from the mains. The system brings hot water from the top, supplying cold, pressurized water to the bottom. This allows the pressure at the taps to maintain constant throughout the cycles. 

Heat Only Boiler

Conventional boilers, also known as heat-only boilers, are similar to system boilers. Like the system boiler, these boilers operate using a cylinder. However, instead of receiving pressure from the mains, this system is under pressure due to gravity. 

With these systems, the cold water supply tank is usually positioned in a higher location in the house, such as the loft. Since the tanks are separate, there’s one hot water cylinder at a lower point, with the cold water supply tank at a higher location. 

Is Water Leaking?

One of the most common reasons for turning off the water supply is a leak somewhere in the water system. If you find a leak in your boiler, storage tanks, or somewhere else in the system, your first step is to turn the water off at the stop cock. 

For most folks, the stop cock is located underneath the kitchen sink. However, it could also be outside, potentially on the pavement. If it’s outside, you might need to contact your water authority (water company) to access it, as it might be shared between you and your neighbors. So, you might need a special key to open the cover. 

Place a bucket underneath the leak (if possible, otherwise, use a towel), then switch off the boiler and isolate the electricity at the fuse box. It’s important to note that turning off the water might not stop the leak immediately. For example, if the tank is leaking, it will likely empty itself.  

Is It Safe To Turn Off The Water Supply?

You might be worried about how turning off the water supply will affect your boiler. However, boilers manufactured today have a plethora of sensors and controls that prevent the boiler from becoming damaged due to a lack of water. 

If these systems didn’t have the sensors they do, turning off the water supply could damage the boiler. The combination boiler would be the worst affected, as its heat exchanger might suffer. The cylinder and radiators would be fine, but the heat exchanger might not fare so well. 

However, you don’t need to worry about adverse effects on your boiler from turning off the water supply. As long as the boiler is in good working condition, turning off the water shouldn’t pose a threat. For example, modern combination boilers will shut down automatically if the sensor detects a drop in mains pressure or if the temperature in the system climbs too high (such as without a supply of cold water).

System and heat-only boilers hold up well, too. They shouldn’t be damaged even if you turn off the water at the mains. Both will continue to heat up at the radiators, and it’s possible you might get a small amount of hot water out of the cylinder. However, it would dry up rapidly since there isn’t any pressure or new water entering the system. The system will continue as if nothing has changed unless you turn on a hot tap. Even then, the fixture will not affect the system, or the boiler will shut down to protect itself. 

All in all, the risk of damage due to turning off the water is very low. So, as long as the system is functioning fine otherwise, turning off the water to repair a leak shouldn’t be a problem. Of course, you can always reach out to a professional in your area for advice or assistance troubleshooting the problem!

Frequently Asked Questions (FAQs)

Is There A Likelihood Of My Pipes Freezing?

Some folks choose to turn off their water supply before leaving home for a few weeks or months in the winter. The logic behind doing so is to prevent a burst water main caused by frozen pipes. 

While this is a good safety measure to isolate the water mains, remember that if the pipes were to freeze and burst before the stopcock, the water would start to pour out once it thaws. The leakage could create quite the problem depending on where this is (inside or outside your home). 

If you regularly leave your home for long periods in the winter, it might not hurt to invest in a smart thermostat. This way, you can remotely control your home’s temperature, keeping it high enough to prevent it from getting too cold and causing condensation. This will help protect the plumbing in your home, especially the pipes running along exterior walls.

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